The present invention relates to a metal ion source comprising a gas-filled ion chamber for producing gas ions, which are accelerated onto a metallic component consisting of the metal intended to give off the metal ions and which, upon hitting the metallic component, release metal atoms therefrom, the metal atoms being, in turn, ionized.
The present invention also relates to a method of generating metal ions, which is especially useful for implanting ions into semiconductor wafers for producing doped semiconductor structures, in which case gas ions are first produced, whereupon the gas ions are accelerated onto a metallic component consisting of the metal intended to give off the metal ions, whereupon metal atoms are released from the metallic component when the gas ions impinge thereon, the metal ions being then ionized.
In the field of semiconductor technology, so-called sputter sources are used, e.g., for applying metal to the surfaces of semiconductor wafers. This metal, which can, for example, be gold or platinum and which is applied to the surface of a semiconductor wafer by sputtering, is diffused into the semiconductor body after having been applied to the surface thereof so that a specific doping and, consequently, a specific reduction of the lifetime of minority carriers is achieved.
In the case of a known sputter source, argon ions are first produced within an ion chamber and within a first electric field. A target consisting of the donor metal, which is intended to give off the metal ions, is positioned in a separate structure within the ion chamber and has applied thereto a separate potential for generating a separate electric field within which the gas ions are accelerated onto the target for the purpose of releasing metal atoms. Also the subsequent ionization and post-acceleration of the sputtered metal atoms takes place in a separate electric field, which is independent of the electric field used for ionizing the argon gas.
The known metal ion source in the form of the above-described sputter source must be equipped with at least two high-voltage sources, which are independent of each other, which makes the known metal ion source technically complicated and expensive. Furthermore, at least two separate electrode leads with adequate insulating devices must be provided; in the case of the metal ion sources of the type in question, these insulating devices must be complicated ceramic insulating devices. In addition, implantations of very small metal doses in the order 10.sup.14 cm.sup.2 which are required for lifetime doping in the case of semiconductors, prove to be difficult in the case of the known metal ion source.
Furthermore, metal vaporization methods and metal vaporizing sources are known, by means of which metal can be deposited on a body to be coated. Examples of these technologies are described in German patent 2827647, German Auslegeschrift 2521536, German Auslegeschrift 2364379 as well as German Offenlegungsschrift 1765636. In the evaporation technique of German OLS 1765636, a rod of the metallic component to be evaporated is arranged in the vicinity of a heating spiral, and a high d.c. voltage potential is used between the heating spiral and the rod of the material to be evaporated. However, such evaporation technologies are neither suitable for implanting very small metal doses of the above-mentioned magnitude, nor can they be used in the case of all compounds, since e.g. the metal platinum does not contain suitable compounds on the basis of which it would be possible to evaporate platinum at the temperatures of approximately 800.degree. C. prevailing within an evaporation source at a sufficiently high vapor pressure.